1. Field of the Invention
The invention relates in general to a mounting method of a passive component, and more particularly to a mounting method of a passive component for solving the tombstone problem of the passive component caused by uneven pulling force that the melted solder applies to the two ends of the passive component.
2. Description of the Related Art
In the present package manufacturing process or the assembly process, the passive component is mounted alone or together with other components on the substrate or circuit board according to the demand. The surface mount technology (SMT) is the most common mounting method nowadays because of the advantages including fast manufacturing speed, high precision and high repeatability.
Please referring to FIGS. 1A˜1C, a conventional surface mounting method is illustrated in FIGS. 1A˜1C. First, as shown in FIG. 1A, solder paste 14 is printed on each contact pad 12 disposed on a surface of a substrate 10 (or circuit board) in a stencil printing process. Next, as shown in FIG. 1B, two ends of a passive component 16 are placed on the solder paste 14 disposed on the surfaces of the contact pads 12. Then, as shown in FIG. 1C, the solder paste 14 is melted and then solidified in a reflowing process for bonding the passive component 16 onto the substrate 10, so that the passive component 16 is electrically connected with the contact pads 12 of the substrate 10.
However, the amount of the solder paste on each contact pad in the present surface mount technology is often slightly different due to the inaccuracy of the manufacturing process. For example, the size of each opening of the stencil is not always the same, and the stencil and the substrate may not be positioned accurately. As a result, the pulling force that the melted solder applies to the two ends of the passive component is uneven in the reflowing process. Or, the uneven pulling force may be caused when the passive component is misaligned on the contact pads. When the pulling forces applied to the two ends of the passive component are not equivalent, the passive component is not positioned accurately. The slight inaccuracy of the positioning process of the passive component usually does not affect the product quality and the yield rate a lot.
However, as the electronic products become more compact and light-weight, all the components become smaller accordingly. The passive component is no exception. When the passive component becomes smaller, the uneven pulling force that the melted solder applies to the two ends of the passive component affects the mounting process more, especially in the passive component with size smaller than size of grade 0402. Please refer to FIG. 2. The tombstone phenomenon defined as the raising of one end of the passive component takes place when the pulling force that the melted solder applies to the two ends of the passive component is uneven. The conventional surface mounting method fails, and the yield rate is decreased. Therefore, a mounting method of a passive component with size smaller than size of grade 0402 is desperately needed to solve the tombstone problem of the passive component caused by uneven pulling force that the melted solder applies to the two ends of the passive component.